37,665 research outputs found
A Cellular Automaton Model for the Traffic Flow in Bogota
In this work we propose a car cellular automaton model that reproduces the
experimental behavior of traffic flows in Bogot\'a. Our model includes three
elements: hysteresis between the acceleration and brake gaps, a delay time in
the acceleration, and an instantaneous brake. The parameters of our model were
obtained from direct measurements inside a car on motorways in Bogot\'a. Next,
we simulated with this model the flux-density fundamental diagram for a
single-lane traffic road and compared it with experimental data. Our
simulations are in very good agreement with the experimental measurements, not
just in the shape of the fundamental diagram, but also in the numerical values
for both the road capacity and the density of maximal flux. Our model
reproduces, too, the qualitative behavior of shock waves. In addition, our work
identifies the periodic boundary conditions as the source of false peaks in the
fundamental diagram, when short roads are simulated, that have been also found
in previous works. The phase transition between free and congested traffic is
also investigated by computing both the relaxation time and the order
parameter. Our work shows how different the traffic behavior from one city to
another can be, and how important is to determine the model parameters for each
city.Comment: 14 pages and 13 figures (gzipped tar file). Submitted to
Int.J.Mod.Phys.C. Minor changes, specially at references and typoes, plus a
clearer summary of the CA rule
A deterministic sandpile automaton revisited
The Bak-Tang-Wiesenfeld (BTW) sandpile model is a cellular automaton which
has been intensively studied during the last years as a paradigm for
self-organized criticality. In this paper, we reconsider a deterministic
version of the BTW model introduced by Wiesenfeld, Theiler and McNamara, where
sand grains are added always to one fixed site on the square lattice. Using the
Abelian sandpile formalism we discuss the static properties of the system. We
present numerical evidence that the deterministic model is only in the BTW
universality class if the initial conditions and the geometric form of the
boundaries do not respect the full symmetry of the square lattice.Comment: 7 pages, 8 figures, EPJ style, accepted for publication in European
Physical Journal
Application of the SRI cloud-tracking technique to rapid-scan GOES observations
An automatic cloud tracking system was applied to multilayer clouds associated with severe storms. The method was tested using rapid scan observations of Hurricane Eloise obtained by the GOES satellite on 22 September 1975. Cloud tracking was performed using clustering based either on visible or infrared data. The clusters were tracked using two different techniques. The data of 4 km and 8 km resolution of the automatic system yielded comparable in accuracy and coverage to those obtained by NASA analysts using the Atmospheric and Oceanographic Information Processing System
Fully-coupled analysis of jet mixing problems. Part 1. Shock-capturing model, SCIPVIS
A computational model, SCIPVIS, is described which predicts the multiple cell shock structure in imperfectly expanded, turbulent, axisymmetric jets. The model spatially integrates the parabolized Navier-Stokes jet mixing equations using a shock-capturing approach in supersonic flow regions and a pressure-split approximation in subsonic flow regions. The regions are coupled using a viscous-characteristic procedure. Turbulence processes are represented via the solution of compressibility-corrected two-equation turbulence models. The formation of Mach discs in the jet and the interactive analysis of the wake-like mixing process occurring behind Mach discs is handled in a rigorous manner. Calculations are presented exhibiting the fundamental interactive processes occurring in supersonic jets and the model is assessed via comparisons with detailed laboratory data for a variety of under- and overexpanded jets
Annealing of Neutron-irradiation-induced Changes in Impurity Conduction in Antimony- Doped Germanium
Annealing of neutron-irradiation-induced changes in impurity conduction in antimony-doped germaniu
Application of an automatic cloud tracking technique to Meteosat water vapor and infrared observations
The automatic cloud tracking system was applied to METEOSAT 6.7 micrometers water vapor measurements to learn whether the system can track the motions of water vapor patterns. Data for the midlatitudes, subtropics, and tropics were selected from a sequence of METEOSAT pictures for 25 April 1978. Trackable features in the water vapor patterns were identified using a clustering technique and the features were tracked by two different methods. In flat (low contrast) water vapor fields, the automatic motion computations were not reliable, but in areas where the water vapor fields contained small scale structure (such as in the vicinity of active weather phenomena) the computations were successful. Cloud motions were computed using METEOSAT infrared observations (including tropical convective systems and midlatitude jet stream cirrus)
Coupling between static friction force and torque for a tripod
If a body is resting on a flat surface, the maximal static friction force
before motion sets in is reduced if an external torque is also applied. The
coupling between the static friction force and static friction torque is
nontrivial as our studies for a tripod lying on horizontal flat surface show.
In this article we report on a series of experiments we performed on a tripod
and compare these with analytical and numerical solutions. It turns out that
the coupling between force and torque reveals information about the microscopic
properties at the onset to sliding.Comment: 7 pages, 4 figures, revte
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